Stacking mats will jack VTA so far out of kilter I'm amazed anyone who cares at all about sound quality would even consider it. Especially since what it means is trying to center the record by hand.
So imagine, you got a record on a stack of mats 1/4" high, which means VTA off by a whopping 1/4", playing a record wobbling around - and this is at 78rpm! Crazy!